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Has anyone out there got any detailed service information for this instrument they could share please? I have a faulty unit and I believe that the problem lies in the 35665-66504 Ch2/A to D board.

I originally attempted a repair some time ago without success so I left the instrument alone for about 2-3 months. When I got round to it again it did successfully initialise twice but then the fault reappeared. The trouble shooting procedures I have indicate that the 66504 board is responsible.

I have inspected both the main power supply and the on-board regs (of the 66504 assy.), they all seem to be working OK but the instrument will not successfully complete its internal cal. A circuit of the 66504 board would, at this point, be a really great help in progressing this repair. Thank you

Could be wrong but your 3566A looks of the age where HP's excellent service manual's, schematics etc
were no longer made as board swapping became the norm. Older gear tends to have manual's available at the usual places, but I checked the places I usually go, nada. Probably a daft question but have you tried contacting Keysight?

Keysight say they can calibrate them but no longer repair them. This will mean that field service was board swapping, that stocks of boards have either run out or been scrapped, and that component level repairs would only have been done on new boards in the manufacturing process (Loveland, Colorado) so component-level info probably won't have ever left the factory. Component level data was collected into a CLIP set for each assembly - Component Level Information Package.

Your best bet may be the HP user groups and ex-HP communities in the US.

David

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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

Very little information on HP kit after late 1980s. I recently had to reverse engineer one of their digital scopes because there is no info for it. I couldn't repair it in the end as there was a cracked board under the attenuator where it had been dropped, so scrapped the entire unit and am selling bits of it for parts. That was unfortunately the only way out.

On the HP scope, I found a number of issues including a dead opamp before I came to that conclusion. As it's an ADC board, worth checking references and any buffer amplifiers for those references to make sure none are being pulled low, assuming there are any. This will affect the input range of the ADC and prevent cal. I've noticed a common theme with HP kit is they have a fixed reference, say 5V and then use a precision opamp to pull that down to 2.5V, buffer it with a heavily compensated opamp and provide that as a ref for any ADC.

I did this with a continuity tester, scope and some patience tracing out the entire analogue front end. Took about 3 days' of evenings to get that far.

Quick google for that particular HP instrument suggests it's card frame based which makes it even more difficult to trace out unfortunately, at least without a riser card available.

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